Manufacture of natural-gas gasoline



Patented dan. 13, 1925.

HAROLD E. THOMPSON, OF CLENDENIN, WEST CARBON CHEMICALS CORPORATION, A

VIRGINIA, ASSIGNOR T CARBIDE AND CORPORATION OF NEW YORK.

MANUFACTURE 0F NATURAL-GAS GASOLINE.

Application led May 31,

To NZZ whom t may concern.'

Be it. known that l. HAnoLnE. THoMrsoN,

a citizen of the United States. residing at Clcndenin. in thc county of Kanawha and 3 State of lest Virginia,have invented certain new and useful Improvements in the Manufacture of Natural-Gas Gasolineot which the following is a specification.

The invention is a process for the manufacture of natural gas gasoline.

In Patent 1,429.175, issued to me on Sept. 12, 1922. I have described and claimed certain procedure for reducing the vapor pressure of wild gasoline to such a value that a transportable and marketable liquid results, such reduction of vapor pressure being effected by the selective removal of those constituents of the wild mixture which have the strongest tendency to increase vapor 2@ pressure, whereby the requisite reduction of vapor pressure is obtained with the withdrawal of a minimum quantity of material, and the stable s alable residue, the gasoline, is produced in maximum quantity. In the patent, have referred particularly to the stabilization or" the wild product resulting from the' well-known compression and oilab'sorption gasoline processes.

rlhere is another natural gas gasoline process which has advantages that are now gaining general recognition, viz, the solidabsorbent process, in which thev gas is brought into Contact with an active=solid absorbent, such as activated carbon, to remove its gasoline constituents, the latter being then recovered .from the solid absorbent by steaming or other treatment adapted to cause the absorbed material to be liberated.

The solid-absorbent process as noW usually practised gives, lilre the older processes, an initial product which is much too wild to be marketed. and an additional treatment is required to stabilize this product. When the stabilizing process consists of.weathering as practised prior to my invention, then the advantages of the solid-absorbent process cannot be fully realized. Absorbents such as activated carbon absorb gasoline constituents with such avidity that it is possible to remove substantially all of the gasoline constituents, including butane, from the gas, but here again prior weathering rocesses impose a serious limitation, an the 1923. serial No. 642,624.

increased yield which would be expected to result. from the use of a highly active absorbent is not fully attained. This is because with an increased absorption of gasoline constituents, there is also an increased absorption of more volatile substances, which go into the wild product and increase its vapor pressure excessively. The Weathering treatment required to reduce the vapor pressure suiiiciently must then be very drastic, with the result that much of the true gasoline constituents are vaporized along with the undesired substances and lost.. The inherent advantage of an unusually active absorbent is thus in a measure nullied.

The present application covers a species of my invention which differs from the embodiment specically claimed in my patent referred to, in that I now describe and claim a process wherein wild gasoline is produced from gas by the use of an acive solid absorbent, and this product is stabilized by application of the principles set-out in the patent. The invention will now be explained in connection with the accompanying diagrammatic drawing.

ln the drawing, the natural gas, by means of suitable piping and valves, is brought into contact with solid absorbent in one or more of the absorbers A. The stripped gas passes ofi" from the absorber to the place 'of use.

1When the material in an absorber has reached the desired degree of saturation, it-

is out out of the gas current and its absorbed materia-lis expelled, as by passing in steam (which may be superheated) from a boiler or by any suitable method. The expelled material together with the steam, if used, pass at a. pressure slightly above barometric to a cooler Where they are suiiciently cooled to condense most of the contained moisture Without, however, liquefying any lconsiderable proportion of the gasoline constituents. A suitable temperature for this purpose is about 175 F. The water separating in the cooler is removed b propriate trap and the gas stil under slight pressure is passed to a first condenser where its temperature is further reduced, say to about 70 F. This latter cooling results in the condensation of a portion vof an apthe contained hydrocarbon material which collects in the receiver, marked Absorption gasoline receiver on the drawing, as a relatively quiet and non-volatile condensate.

The portion of the hydrocarbon material which is not liquefied in the first condenser is compressed to about 100 pounds per square inch, the compressed gas being again cooled to the temperature of cooling water in the second condenser, whereupon a further portion of hydrocarbon material is liquefied and collected in the receiver marked Compression gasoline receiver on the drawing. This latter condensate, being formed at a pressure of several atmospheres, will of course be more volatile or wild than the absorption gasoline.

A portion of the hydrocarbon material will remain uneondensed even at a pressure of 100 pounds per square inch and at the temperature of cooling` water, and this material will escape through a pressure regulator set to hold the desired pressure in the compression gasoline receiver and may then be mixed with the stripped gas or utilized for any other purpose. The two liquid hydrocarbon fractions are then treated in a single rectifying column in accordance with the principles set forth in my patent referred to above.

The absorption gasoline being relatively non-volatile, requires but little rectification and is therefore introduced into the rectifying column at a point considerably removed from its top. The more volatile compression gasoline is introduced into the rectifying column at a higher point in order that it may subjected to a more thorough rectification as it descends in the column.

The requisite cooling of the top of the' column is secured by the absorption of heat which takes place upon expanding the compression gasoline into the column, the pressure change being for example from 10() pounds per square inch to a pressure only' slightly above barometric pressure.

The volatilehydrocarbons leaving the rectifying column as vapors, and comprising for example those constituents of natural gas `which are more volatile than butane, will pass through a heat-exchanger wherein they serve to cool the incoming compression gasoline, and are then discharged into the stripped gas line or other place of use.

Except as noted, the operation of the rectifying column is identical with that dis- ,closed in my patent referred to above, the

vapor tension of the finished gasoline being -readily adjusted by the rate at which heat is supplied to the heating coil of the kettle of the rectifying column. The characteristic's of the product being formed can be determined at any time by an observation. of the temperature of the material passing from the kettle to the rectifying column, and of the pressure at which the gaseous product of the rectifying column leaves the appara-tus. v

In'the rectifying column, the wild mixture is separated into a vaporus fraction, and a liquid fraction which constitutes the final product, and the se )aration is so made that the vaporous fractlon and the liquid fraction do not contain a substantial quantity of more than one hydrocarbon individual 1n common.

For a maximum yield of marketable gasoline, the material may be separated so that substantially all the butane enters the liquid while all more volatile hydrocarbons are boiled ofi". Of course, some of the butane may be removed from the liquid with the propane and other relatively volatile h vdrocarbons, and a less volatile final product will result. It will usually be impossible to incorporate into the final product a substantial quantity of a hydrocarbon more volatile than butane, assuming that the product is to be transported and used as natural gas gasoline now is, The sum of the effects of the large quantity of butane and of the more volatile hydrocarbon would be too large to permit the material to pass any usual vapor-pressure specifications.

By excluding all hydrocarbons more volatile than butane from the final product, its vapor pressure will often remain within permissible limits when all the butane in the gas treated is caused to enter the gasoline. That is to say, the gasoline produced in such cases is of acceptable quality, and a maximum yield is obtained, when all the butane of the gas is incorporated into the gasoline. Full advantage may therefore be taken of the high activity of the absorbent, since the rectification treatment affords a means, not heretofore available, of selectively and quantitatively removing the hydrocarbons more volatile than butane.

Many of the natural gases now used for the recovery of gasoline contain a percentage by weight of butane which is larger than the combined weight-percentages of all hydrocarbons of higher molecular weight than butane. If all the butane and less volatile substances contained in such gases are incorporated into the final product, a gasoline containing upward of 50% butane will result. Nevertheless, due to complete absence of substances more volatile than butane, the vapor pressure will often not exceed 18 pounds per square inch at 100 F., and the product will be readily salable as gasoline. So far as I am aware, no natural gas gasoline containing as much as 25% butane and free from propane and all other substances more volatile than butane had been produced prior to my invention, nor had there been produced any natural gas gasoline containing as much as 25% butane and having a vapor pressure as low as 18 poundslper square inch at 100 F.

In a particular instance, a gasoline produced in accordance with my invention contained 46.2% butane, the balance being pentane and less volatile hydrocarbons, With hydrocarbons more volatile than butane absent. Despite this high butane content, the vapor pressure of the product was only 13 pounds per square inch at- 100o I?. Natural gas gasolines having any such relation of butane content to vapor pressure were unknown prior to my invention.

It Will be seen that by combining' the rectification steps with the solid-absorbent process, the entire butane content of a natural gas can oftener be incorporated into gasoline made. therefrom Without impart-- ing an excessive vapor pressure to such gasoline, While if a product containing substances more volatile than butane, or containing ionly a part of the butane, and no more volatile substances is desired, the combined process Will produce the maximum quantity of such liquid of any given vapor pressure, or a minimum vapor pressure for any given yield of liquid. In this latter case, modification of the final product is accomplished through control of the rectification, the rest of the process Jfollowing without modification or interruption the lines on Which it attains its maximum efficiency.

I claim 1. Process of' making gasoline of predetermined vapor pressure from natural gas,

which comprises treating the gas With an active solid absorbant in such manner that the major portion of the butane and substantially all of the less volatile hydrocarbons are absorbed, liberating the absorbed material from the absorbent, and rectifying it to produce a vaporous and a liquid fraction in such manner that said vaporous i fraction and said liquid fraction do not contain a substantial quantity of more than one hydrocarbon individual in common.

2. Process according to claim 1 in which the solid absorbant is activated carbon.

3. Process according to claim 1 in Which the liquid fraction produced contains no constituent more volatile than butane.

4. Process of making gasoline of prede termined vapor pressure from natural gas, which comprises treating the gas With an active solid absorbant in such manner that substantially all the b'utane and less volatile hydrocarbons are absorbed, liberatingr the absorbed material from the absorbent, and rectifying it to produce a Vaporous and a liquid fraction in such manner that said Vaporous fraction and said liquid fraction do notcontain a .substantial quantity of more than one hydrocarbon individual in common.

5. Process according to claim 4 in which the solid absorbant is activated carbon.

6. Process according to claim 4 in which the liquid fraction produced conta-ins no constituent more volatile than butane.

7. Process of making gasoline of predetermined vapor pressure from natural gas, which comprises treating thegas with an active solid absorbent in such manner that substantially all the lontane and less volatile hydrocarbons are absorbed, liberating the absorbed material from the absorbent and rectifying it to produce a vaporous and a liquid fraction in such manner that no constituent occurs in substantial quantity in both said fractions.

8. Process according to claim 7 in which the solid absorbent is activated carbon.

9. Process according to claim 7 in which the liquid fraction pnoduced contains no constituent more. volatile than butane.

In testimony whereof, I affix my signature.

HAROLD E. THOMPSON. 

